Control apparatus



5. E. EGESDAL CONTROL APPARATUS Filed Dec. 23, 1966 mpmmum March 10, 1970 MJ N mzoN I N \-"ENTOR. SANFORD E. EGESDAL ATTORNEY United States Patent F 3,500,394 CONTROL APPARATUS Sanford E. Egesdal, Des Plaines, Ill., assignor to Honeywell Inc., Minneapolis, Minn., a corporation of Delaware Filed Dec. 23, 1966, Ser. No. 604,382 Int. Cl. G08b 29/00 US. Cl. 340-409 3 Claims ABSTRACT OF THE DISCLOSURE An alarm system having a central station and a remote station, the remote line connecting the two stations having a supervisory current flowing therethrough and the remote line being terminated at the remote station by an end-of-line Zener diode through which the supervisory current normally flows. An open circuit or a short circuit in the supervised line is effective to actuate alarm means at the central station.

SUMMARY OF THE INVENTION An alarm device having a central station, a remote station, adapted to be interconnected by a supervised line in which the line is terminated at the remote station by a Zener diode connected across the line. A supervisory current normally flows through the line and a change in this current from a normal value is effective to actuate an alarm at the central station.

DRAWING The single figure of the drawing is a schematic representation of a preferred embodiment of the invention.

DETAILED DESCRIPTION Referring now to the drawing there is disclosed generally a multizone alarm system having at a central or supervisory station individual zone responsive circuits 10, 11 and 12 and a common circuit 13. In the common circuit 13 a source of AC is converted to DC by rectifier 14 and smoothed by filter 15 to provide a filtered positive DC potential on conductors 16 and 17 with respect to common negative conductor 20. The output of rectifier 14 is connected by way of a normally closed reset switch, a junction 19, and a rectifier 18, which rectifier normally is bypassed by a jumper, to the filter 15 and conductor 16. Conductor 17 is connected at junction 19.

The conductor 16 is connected through a Silence switch and a resistor 21 to the anode of a current switching SCR the cathode of which is connected to negative conductor 20. In parallel with resistor 21 is a serially connected diode 22 and Buzzer. In parallel with the Buzzer is connected the winding of a relay K Triggering the SCR to conduction energizes the Buzzer and relay K The conductor 17 is connected to the anode of an SCR A load circuit for the SCR, is connected in the cathode circuit and comprises in parallel a resistor 23 and an indicator light 24. Also in parallel with these elements is a serially connected diode 25 and relay winding K This load circuit is connected between negative lead 20 and the cathode of SCR The cathode of SCR is also connected through a pulse circuit comprising a diode 26, a capacitor 27, a junction and a resistor 31 to the gate electrode of SCR Further filtering of the DC voltage by capacitor 32, resistor 33 and Zener diode 34 provides a Well regulated voltage (15 volts for example) on conductors 35 and 20 for a pair of terminals, 36 and 36'. The terminals 36 is connected by a resistor to the negative line 20.

A transmission line or remote line 37, 37', which is to be supervised, interconnects these terminals 36, 36'

and a remote station generally indicated at 40. The remote station 40 which terminates the line 37, 37 may include elements such as a normally open condition responsive switch 41, a normally closed condition operated switch 42, a break-before-make transfer switch 43 and does include as an important element of the invention, an endof-line Zener diode 44. This Zener diode has a Zener breakdown voltage which is less than the regulated voltage at terminal 36. In the present example it may be a 10-volt Zener diode. The elements 41, 42 and 43 may be fire responsive, burglar responsive or the like.

One further current path may be traced from the regulated potential at conductor 35 through a voltage dropping resistor 50, and a junction 51 to the collector of an NPN transistor 52. The emitter of transistor 52 is directly connected to line 20. A resistor 53 connects the terminal 36' to the base or control electrode of transistor 52. The terminal 36' is further connected through a forward diode 54, a junction 55 and a Zener diode 56 to the gate of SCR Another diode 57 connects the junction 51 to the junction 55.

In considering the operation of the alarm it should generally be understood that the apparatus is designed so that a quiescent supervisory current normally flows from the central station through the remote line to the remote station end-of-line Zener diode and back, and that a change in this current due to an open in the line or a short across the line operates the alarm for the zone. Specifically, the regulated 15 volts on line 35 causes a current to flow from terminal 36 at the central station, through remote line 37, through the normally closed condition responsive switches 42 and 43 in series with the line, through the end-ot-line Zener diode 44, back through line 37' to terminal 36'. At terminal 36' the current path divides with a portion flowing through resistor 45 to conductor 20 and a second portion flowing through the parallel path comprising resistor 53 and the base-to-emitter control or input circuit of transistor 52. The 10-volt end-of-line Zener diode 44 tends to maintain a 10 volt differential between lines 37 and 37' so that terminal 36' is normally approximately 5 volts positive with respect to conductor 20. A 5-volt potential at terminal 36' is thus normal and is effective to maintain transistor 52 conductive so that no triggering of SCR will occur.

Let it now be assumed that a short occurs across the lines 37 and 37'. This may occur due to a cross on the lines or by the operation of the condition responsive switch 41. The end-of-line Zener diode 44 is then bypassed and the voltage on line 37' rises to approximately 15 volts. This rise in voltage is sufficient to exceed the breakdown voltage of Zener diode 56 and a current flows from terminal 36, through the shorted line, terminal 36, diode 54, Zener diode 56 and into the gate of SCR triggering it to conduction. When SCR fires, the indicator lamp 24, and the relay K are both energized. In addition a triggering pulse flows through diode 26, capacitor 27, and resistor 31 to trigger SCR The conduction of SCR energizes the audible Buzzer and energizes relay K Since both SCR and SCR are energized from a filtered DC source they remain conductive until the voltage is removed. The Buzzer can be turned oil? by the Silence switch which can be operated to remove the potential from SCR and allow it to extinguish. SCR, can be extinguished by operating the Reset switch which removes the anode potential from it. If the short has been corrected the SCR will remain off when reset.

Let it now be assumed that an open circuit occurs in the remote station or in the line 37, 37. Current then ceases to flow in the input circuit of transistor 52 and the transistor turns off whereupon the collector voltage rises towards 15 volts. Current then flows from the junc- 3 tion 51 through diode 57 and Zener diode 56 to trigger SCR Thus it may be seen that either an open circuit or a short circuit in the supervised line 37, 37' causes SCR to fire which in turn fires SCR Under certain conditions it is preferred to operate the apparatus with rectifier 18 operative by removing the jumper paralleling it. In this modified mode of operation a positive filtered DC potential still appears on conductor 16 as before, but there is now applied to conductor 17 an unfiltered pulsating DC potential which varies from zero volts to maximum volts every half cycle of the AC source. This provides for automatic reset of the alarm when the line 37, 37' is returned to normal after an alarm condition. Since the potential on conductor 17 is reduced to zero volts momentarily twice each cycle of the AC source, SCR is extinguished and refired twice each cycle while a triggering voltage is applied. As soon as the triggering potential to SCR through Zener diode 56 disappears thereby indicating the line 37, 37' has returned to normal, the SCR extinguishes and remains 01f. In this mode of operation even though a pulsating current flows in SCR during alarm conditions, the capacitor in parallel with relay K tends to smooth the current flow through the relay coil. Diode 25 decouples the relay and capacitor from SCR The embodiments of the invention in which an exclusive property or right is claimed are defined as follows:

1. In an electrical supervisory device for supervising a line having a supervisory station and a remote station adapted to be interconnected by the line, the combination comprising:

a supervisory station;

a remote station comprising a terminating Zener diode, said remote station being adapted to be connected to said supervisory station by a pair of conductors;

a source of potential at said supervisory station having a potential magnitude in excess of said Zener diode breakdown potential, said source being adapted to be connected to said conductors to provide a normal current level through said Zener diode;

and current responsive means connected to be responsive to an abnormal current from said source whereby upon the event of an abnormal current flowing toward said remote station said current responsive means is operated, said current responsive means comprising:

current switching means comprising a triggering circuit and an output circuit; transistor means connected to receive a bias current which is a function of said current level; impedance means energizing said transistor means output circuit from said source; first diode means including further Zener diode means connecting said transistor means output circuit to said triggering circuit; second diode means including said further Zener diode means connecting said first Zener diode to said triggering circuit, so that upon the occurrence of said abnormal current at least one of said first and second diode means is rendered conductive to apply a signal to said trigger circuit of said current switching means. 2. The supervisory device according to claim 1 in which said current responsive means is connected in a series loop with said source and said Zener diode.

3. The supervisory device according to claim 1 in which said current responsive means includes alarm means operated upon the event of said abnormal current.

References Cited UNITED STATES PATENTS 3,195,043 7/1965 Burig et al.

3,230,440 1/1966 Kleiner 3173l X 3,254,334 5/1966 Mitchell 340-276 3,304,547 2/1967 BriStOl 340276 X 3,311,907 3/1967 Teal 340-248 3,382,409 5/1968 Assow et al 31731 X OTHER REFERENCES IBM Tech. Disc. Bul., vol. 3, No. 6, November 1960, p. 37, Voltage Detection Circuit, F. L. O"Malley.

JOHN W. CALDWELL, Primary Examiner D. L. TRAFT ON, Assistant Examiner US. Cl. X.R. 

